1. Field of the Invention
This invention relates generally to the field of plastic containers, and more particularly to plastic containers that are designed to accommodate the volumetric expansion and contraction that is inherent to the hot-fill packaging process.
2. Description of the Related Technology
Many products that were previously packaged using glass containers are now being supplied in plastic containers, such as containers that are fabricated from polyesters such as polyethylene terephthalate (PET).
PET containers are typically manufactured using the stretch blow molding process. This involves the use of a preform that is injection molded into a shape that facilitates distribution of the plastic material within the preform into the desired final shape of the container. The preform is first heated and then is longitudinally stretched and subsequently inflated within a mold cavity so that it assumes the desired final shape of the container. As the preform is inflated, it takes on the shape of the mold cavity. The polymer solidifies upon contacting the cooler surface of the mold, and the finished hollow container is subsequently ejected from the mold.
Hot fill containers are designed to be used with the conventional hot fill process in which a liquid product such as fruit juice is introduced into the container while warm or hot, as appropriate, for sanitary packaging of the product. After filling, such containers undergo significant volumetric shrinkage as a result of the cooling of the product within the sealed container. Hot fill type containers accordingly must be designed to have the capability of accommodating such shrinkage. Typically this has been done by incorporating one or more vacuum panels into the side wall of the container that are designed to flex inwardly as the volume of the product within the container decreases as a result of cooling.
Typically, the vacuum panel regions of conventional hot fill containers are characterized by having surfaces that are designed to deflect inwardly when the product within the sealed container undergoes shrinkage. In some instances, an island may be defined in the middle of the vacuum panel in order to provide support for an adhesive label that may be placed over the container. In other instances, ribs may be molded into the vacuum panel area in order to provide an enhanced grip surface or to enhance the strength of the vacuum panel area. Grippability for the consumer is an important consideration in the design of many containers. In containers that have vacuum panels with gripping structure, the technology for optimizing the efficacy of the gripping structure and the dimensional stability of the container while it is being gripped while at the same time permitting sufficient flexibility to accommodate volumetric changes within the container is still evolving. Minor changes in curvature and geometry may be important to such optimization. Top load strength and efficient utilization of plastic material are also important design considerations for such containers.
Vacuum panels of conventional hot-fill containers, including those vacuum panels that are provided with structure to enhance gripping, typically are designed to be substantially symmetrical about a central vertical axis as viewed in side elevation. PCT Publication WO 2007/041422 discloses such a container having four vacuum panels. In hot-fill container designs that have an even number of vacuum panels, opposing panels are also typically shaped to be substantially symmetrical about the center axis of the container.
A need has existed for an improved hot fill container design that possesses optimal capacity to accommodate volumetric expansion and contraction, grippability and dimensional stability while being gripped.